A modern petroleum refinery is designed to maximize the production of select liquid products from crude oil. In addition to the well known atmospheric and vacuum distillation processes used to provide refined products, many refineries utilize petroleum cokers to further process the residual materials remaining after distillation. The three common coking processes, fluid, flexi and delayed coking, have been used for decades. As such the common operating conditions for petroleum coking are well known throughout the industry.
During the fill cycle of the coking process, a foam layer forms on the surface of the feedstock as it fills the coke drum. Operators must control foaming within the coke drums otherwise the foam will enter the overhead vapor line resulting in a blockage. The preferred method for precluding foam-over, requires injecting a silicone based anti-foam agent (AF agent or material) into the drum. According to a tutorial presented by Great Lakes Carbon Corporation at the AIChE 1998 Spring National Meeting, the preferred method for controlling foam requires continuous injection of an AF agent. According to the tutorial, “a Dow Chemical Company representative stated in 1981 that it is easier to prevent a foam than it is to kill a foam.” The tutorial further noted that continuous injection reduces the problems associated with foam and reduces the quantity of anti-foam agent required.
Management of the silicone anti-foam agent injection is critical as any carry-over of the silicone material through the overhead vapor line will poison the catalyst found in downstream operating units such as the hydrotreating unit. Thus, operations which use too little silicone based AF agent may foam-over and carry the silicone downstream. However, excessive usage of silicone based AF agent, due to continuous injection, increases costs, may reduce the production of valuable liquids and may lead to an undesirable coke material.
Clearly, further improvements are desired in the current coking process. In particular, improved processes which control foaming in order to enhance liquid yield while improving the coke material are desired. Further, a coking foam control method which does not utilize a silicone based AF agent will particularly enhance the coking process.